CX7 Power Supply Board
Including Factory Revision C
There has been much discussion about the CX7 power supply
boards. Here is what I have learned so far.
The original board used many discrete transistors and TIP series transistors (rear chassis mounted) to regulate the various voltages.
As we all know these boards were very much prone to failure. Early on there was a modification available to remove the pass transistors on the board
and replace the TIP transistors with IC regulator chips. This modification was done by many owners and worked quite well. Here is a schematic that I created many years ago. It is what I use anytime I make a power supply mod.
Click this link for the schematic - CX7 Power Supply - IC Mods
There are 3 other iterations of the board and information on them is limited. I will refer to them by the most accepted name we use to describe them.
The "W2PV Board" required a total rewire of the power supply.
It used a large Molex connector mounted to the board.
Why anyone would have used this board is beyond my capacity to reason. Installation of this board destroyed the wiring integrity of the radio.
I have removed one of these boards from a CX7. The modification was abandoned but not before the wiring harness was destroyed.
And I have seen one other CX7 with this board that is apparently working.
Here is a link to some information on this modification and other W2PV mods courtesy of Brian, NI6Q.
There is another board that was well built. It used a TO-3 style regulator mounted to a heat sink on the board for -15 volts.
This is referred to as the "Johnson Board". I do not know why. Perhaps it was named after the person who created it.
There is a hand drawn schematic available. It was created by Paul Koller, W8CXS.
And there was a true Signal/One modification: 61-S0003-001-C.
This board has a copyright date of 1974.
Very late for any CX7 product. There are several of these boards in CX7s. I have two.
And I just come across some images of unpopulated boards and notes on several of the pages.
I am not certain who made the notes. As far as I know there is no schematic.
Now that I have these board images I am going to carefully note the parts on a print and create a schematic.
There are 3 transistors on the board that are used for regulating one of the voltages. My guess now is +34 volts.
Gary, W0OGM, and I may attempt to recreate some of these boards. More on that later.
Here are the pictures of the Revision C Power Supply. Click on thumbnail for larger image.
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May 02, 2018.
Updated: May 02, 2018
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